The invention pertains to proximity sensor systems. Particularly, it pertains to sensor systems which analyze the impedance of their resonators, and more particularly to such systems in which analyzers eliminate the effects of high levels of electromagnetic interference (EMI) in the sensors' environments.
A class of non-radiating proximity sensors and the associated detection systems rely on inductive properties and rely on the principle that their effective inductance changes in proportion to a conducting object's position.
A common and well-known detection method for this class of sensors is the eddy-current killed oscillator. In this system a circuit, including an inductor in the sensor, is in resonance when there is no detectable object near the sensor. When a detectable object is sufficiently close to the sensor, the change in the effective loss of the inductor in the sensor defeats resonance and thus causes the oscillations in the circuit to cease. If the inductance changes, the resonator may change frequency without quenching the oscillations. It is the change in the loss that spoils the resonance and stops the oscillation. The related-art approach is inadequate for environments with high electromagnetic interference.
The present invention circumvents this problem by utilizing in a particular way the principles of AM radio, without radiating an AM signal, as well as of resonance tracking, namely synchronous demodulation, to analyze the impedances of proximity sensors. The resonance tracking circuit in this invention never stops because the sensor is being driven with a generated waveform, but the change in loss causes the amplitude of the signal to change and ultimately causes the output to change due to the change in amplitude.